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All plants contain tiny amounts of [https://en.wikipedia.org/wiki/Hydrogen_cyanide hydrogen cyanide] (HCN), however some plants also release high amounts of HCN from a class of glycosides called "cyanogenic glycosides". [https://en.wikipedia.org/wiki/Amygdalin Amygdalin] and [https://en.wikipedia.org/wiki/Linamarin linamarin] are common examples of cyanogenic glycosides. After being released from cyanogenic glycosides, HCN is highly toxicto animals. The human body is used to breaking down trace amounts of cyanide into the less toxic substance thiocyanate with an enzyme called rhodanese, which then leaves the body via urination <ref name="Gleadow_2014">[http://www.annualreviews.org/doi/full/10.1146/annurev-arplant-050213-040027 Cyanogenic Glycosides: Synthesis, Physiology, and Phenotypic Plasticity. Roslyn M. Gleadow and Birger Lindberg Møller. 2014.]</ref>. Only Although there are more than 3,000 plant species that are cyanogenic (a number of them cultivated by farmers perhaps because their cyanogenic properties deter animals from eating them), only a few parts of plants release that are considered foods contain enough HCN from cyanogenic glycosides to be considered dangerous (generally, other forms of cyanide are considered more dangerous, such as from exposure to air or water that is polluted with cyanide) <ref name="CDC1">[http://www.atsdr.cdc.gov/toxprofiles/tp8.pdf toxicology Profile for Cyanide. Agency for Toxic Substances & Disease Registry. July 2006. Retrieved 08/25/2016.]</ref>. The location of the cyanogenic glycosides and the enzymes that release them are often each located in different (or all) parts of plants, and those locations are diverse across species. In some plants, the cyanogenic glycosides are concentrated in the stems or leaves of the plant and not the seeds (e.g. sorghum, barley, and lima beans). In fruits sometimes the seeds contain concentrated amounts (e.g. black cherry pits), and other times in the fruit itself (e.g. ''Passiflora edulis''). In rosaceous stone fruits, cyanogenic glycosides are located in the seeds, but the beta-glucosidase enzyme that the plant uses to release HCN is located in the roots of the plant. The concentration of cyanogenic glycosides is generally higher in seedling plants compared to mature plants, however this is there are a few exceptions where this is the opposite (e.g. some ''Eucalyptus'' species, and lima beans). HCN is released from cyanogenic glycosides just like other types of glycosides: beta-glucosidase enzyme or exposure to low pH breaks the bond between a glucose molecule and an unstable compound called "cyanohydrin" (or "alpha-hydroxynnitrile"), which then disassociates into a ketone or benzaldehyde and an HCN molecule. This reaction is stimulated by maceration, and by bacteria in the human gut . The cyanogenic glycosides themselves are not toxic until the HCN is released <ref name="Speijers">[http://www.inchem.org/documents/jecfa/jecmono/v30je18.htm "Cyanogenic Glycosides", First Draft. Dr G. Speijers. National Institute of Public Health and Environmental Protection Laboratory for Toxicology, Bilthoven, The Netherlands. Retrieved 08/25/2016.]</ref>. A lethal dosage of cyanide in humans is estimated to be around 1.52 mg per kilogram of body weight <ref>[http://www.atsdr.cdc.gov/toxprofiles/tp8.pdf toxicology Profile for Cyanide. Agency for Toxic Substances & Disease Registry. July 2006. Pg 42. Retrieved 08/25/2016.]</ref>. High exposure can cause harm to the brain and heart, and can cause comas or death. Exposure to 0.05 mg of cyanide per kilogram of body weight per day for 15-364 days is considered to cause accumulative health risks, such as reproductive, neurological, thyroid, and gastrointestinal issues <ref>[http://www.atsdr.cdc.gov/toxprofiles/tp8.pdf toxicology Profile for Cyanide. Agency for Toxic Substances & Disease Registry. July 2006. Pg 21. Retrieved 08/25/2016.]</ref>.